Cellular approaches to treatment of diabetes appear to correct or improve many aspects of diabetes that intensive insulin therapy cannot, while markedly lowering risk of hypoglycemia. While islet transplantation clearly has multiple conceptual advantages over whole pancreas transplant, clinical success is yet to be realized. New tolerization induction protocols, manipulation of specific T cell sets, and blockade of co-stimulatory pathways have shown exciting results with islet transplants in preclinical (NOD) and primate models. However, these methods require several weeks to condition the recipient before transplant is performed. In addition to cellular rejection, initial islet engraftment is very poor. This is thought to be due to a combination of ischemia, growth factor starvation/apoptosis, and a non-specific inflammatory response. Published data indicates that ex vivo rodent islet manipulations and gene therapy can inhibit these events and facilitate engraftment. Thus, it is necessary to develop methods to maintain human islets in culture until the intended recipient has been immunologically prepared. Human islet modifications may also facilitate engraftment and resistance to non-cognate (and cognate) immune effector systems. The investigators have developed fully defined, serum-free culture systems for long-term culture (greater than 12 months) of human and other species islets. These systems have been independently validated. Preliminary data shows long term cultured human islets are equally effective to immediate transplant in streptozotocin-diabetic SCID. The investigators have also developed completely novel and pilot data using recombinant adeno-associated viral vectors (rAAV) to mediate ex vivo gene therapy and permanent gene expression in intact islets. The rAAV integrate in non-dividing cells, are non-immunogenic and non-pathogenic in humans. The goals of this proposal are to: 1) determine stability and safety of long term cultured primary human islets, 2) evaluate rAAV-mediated ex vivo gene therapy of human islets, and 3) investigate the feasibility of combined macro-phage depletion and rAAV ex vivo gene therapy on treatment of NOD. This study will provide necessary data for accelerated progression to Phase I trials.